Charged particle beam column and method of operating same

ABSTRACT

A charged particle beam column includes a charged particle beam source to generate a charged particle beam; an objective lens to focus the charged particle beam in an object plane; a first condenser lens disposed in a beam path of the charged particle beam between the charged particle beam source and the objective lens; a deflector disposed in the beam path between the first condenser lens and the objective lens and configured to change an angle of incidence of the charged particle beam in an object plane; and an aberration corrector disposed in the beam path between the deflector and the objective lens and configured to compensate aberrations introduced by the objective lens. The aberration corrector is also configured to not compensate aberrations introduced by the first condenser lens.

FIELD

The disclosure relates to a charged particle beam column and to a methodof operating a charged particle beam column, including such columns andmethods where an angle of incidence of a charged particle beam on aspecimen can be varied.

BACKGROUND

A scanning electron microscope (SEM) is know which is configured suchthat an angle of incidence of a focused electron beam onto a specimencan be varied. Using such SEM, it is possible, for example, to obtain afirst image by scanning the specimen with a focused electron beam whilean angle of incidence of the beam on the specimen is set to a firstvalue, and to obtain a second image by scanning the same specimen withthe electron beam while the angle of incidence is set to a second valuedifferent from the first value. From analyzing the two images it ispossible to reconstruct a three-dimensional structure of the specimen.The charged particle beam column can include an aberration corrector tocompensate aberrations caused by condenser lenses and an objective lensof the charged particle beam column due to high tilted angles of thebeam traversing the column including the condenser lenses and objectivelens.

SUMMARY

The present disclosure provides a charged particle beam column and amethod of operating a charged particle beam column, which can provideimproved compensation of aberrations caused, for example, by highlytilted angles of a charged particle beam at a specimen.

In some embodiments, the disclosure provides a charged particle beamcolumn that includes: a charged particle beam source configured togenerate a charged particle beam; an objective lens configured to focusthe charged particle beam in an object plane; a deflector disposed in abeam path of the charged particle beam between the charged particle beamsource and the objective lens; and an aberration corrector configured tocompensate aberrations introduced by components located in the beam pathdownstream of the deflector while avoiding compensation of aberrationsintroduced by components located in the beam path upstream of thedeflector. The aberration corrector is disposed in the beam path betweenthe deflector and the objective lens, which means that the chargedparticles traverse the aberration corrector on their way from thedeflector to the objective lens.

In certain embodiments, the disclosure provides a charged particle beamcolumn that include: an objective lens configured to focus a chargedparticle beam in an object plane; a first condenser lens disposed in abeam path of the charged particle beam upstream of the objective lens; adeflector disposed in the beam path between the first condenser lens andthe objective lens, the deflector configured to change an angle ofincidence of the charged particle beam in an object plane; and anaberration corrector disposed in the beam path between the deflector andthe objective lens. The aberration corrector configured to compensateaberrations introduced by the objective lens, and the aberrationcorrector is configured to not compensate aberrations introduced by thefirst condenser lens.

In some embodiments, the disclosure provides a charged particle beamcolumn that includes: an objective lens configured to focus a chargedparticle beam in an object plane; a deflector disposed in a beam path ofthe charged particle beam upstream of the objective lens; and anaberration corrector disposed in the beam path between the deflector andthe objective lens. The aberration corrector is configured to compensateaberrations introduced by components located in the beam path downstreamof the deflector without compensating aberrations introduced bycomponents located in the beam path upstream of the deflector.

In certain embodiments, the disclosure provides a charged particle beamcolumn that includes: a charged particle beam source configured togenerate a charged particle beam; an objective lens configured to focusthe charged particle beam in an object plane; a first condenser lensdisposed in a beam path of the charged particle beam between the chargedparticle beam source and the objective lens; a deflector disposed in thebeam path between the first condenser lens and the objective lensconfigured to change an angle of incidence of the charged particle beamin an object plane; and an aberration corrector disposed in the beampath between the deflector and the objective lens and configured tocompensate aberrations introduced by the objective lens. The aberrationcorrector is also configured to not compensate aberrations introduced bythe first condenser lens.

In some embodiments, a charged particle beam column can include a secondcondenser lens disposed in the beam path between the deflector and theobjective lens. In such embodiments, the aberration corrector can befurther configured to additionally correct aberrations introduced by thesecond condenser lens, which is located downstream of the deflector.

In certain embodiments, a charged particle beam column can include abeam scanner configured to scan a location of incidence of the chargedparticle beam across the object plane. Additionally or alternatively, acharged particle beam can include a particle detector configured todetect particles emerging from a specimen near the object plane.

In some embodiments, an aberration corrector can include a plurality ofmultipole lens elements. In certain embodiments, an aberration correctorcan include a mirror configured to reflect the charged particle beam.

In some embodiments, the disclosure provides a method of operating acharged particle beam column that includes: condensing a chargedparticle beam while introducing first aberrations into the chargedparticle beam to provide a first condensed charged particle beam;deflecting the condensed charged particle beam to provide a deflectedcharged particle beam; focusing the deflected charged particle beam on aspecimen while introducing second aberrations into the deflected chargedparticle beam; and compensating the second aberrations while leaving thefirst aberrations uncompensated to provide a compensated chargedparticle beam.

In certain embodiments, the disclosure provides a method of operating acharged particle beam column that includes: generating a chargedparticle beam; condensing the generated charged particle beam whileintroducing first aberrations on the beam; deflecting the condensedcharged particle beam; and focusing the further condensed chargedparticle beam on a specimen while introducing second aberrations on thebeam; and compensating the second aberrations while leaving the firstaberrations uncompensated.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing as well as other advantageous features of the disclosurewill be more apparent from the following detailed description ofexemplary embodiments, the drawings and the claims.

FIG. 1 is a schematic illustration of a charged particle beam column;and

FIG. 2 is a schematic illustration of the charged particle beam columnshown in FIG. 1 in a configuration to verify a setting for aberrationcompensation.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the exemplary embodiments described below, components that are alikein function and structure are generally designated by like referencenumerals.

FIG. 1 is a schematic illustration of a charged particle beam column 1.The charged particle beam column 1 shown in FIG. 1 has certainsimilarities with beam columns disclosed in more detail in U.S. Pat. No.7,223,983 B2, the full disclosure of which is incorporated by referenceherein.

The charged particle beam column 1 shown includes a charged particlebeam source 3, which is an electron beam source in the illustratedembodiment. Other embodiments may include sources to generate beams ofother charged particles, such as ions. A beam 5 of charged particlesemitted from the source 3 traverses a condenser lens 7 to converge thebeam 5 towards an aperture plate 9. The aperture plate 9 includes anaperture 11 having a diameter smaller than a diameter of a beam 5incident on the aperture plate 9. The aperture plate 9 allows arelatively narrow collimated portion 13 of beam 5 to traverse theaperture 11 of the aperture plate 9.

Downstream of the aperture plate 9 in the beam path of the beam portion13 there is disposed a deflection system 15 to deflect the beam 13. Asshown in FIG. 1, the deflection system 15 includes two deflectors 16 and17, which are disposed and configured to deflect the beam 13 at twolocations spaced depart along the beam path. In certain embodiments, thedeflection system may comprise a single deflector or three or moredeflectors to deflect the beam at a single location or three or morelocations along the beam path, respectively.

The charged particle beam column 1 also includes a condenser lens 19disposed downstream of the deflection system 15 to further converge thebeam towards an objective lens 21 which is configured to focus the beam13 at a relatively small spot 23 on an object plane 25 at which asurface 27 of a specimen 29 can be arranged for inspection.

The charged particle beam column includes a controller 31 which isconfigured to energize the deflectors 16, 17 of the deflection system 15such that an angle between a direction of the beam 13 at the objectplane 25 relative to an axis 33 of symmetry of the objective lens 21 canbe varied. FIG. 1 shows the beam 13 in full lines to be incident on theobject plane 15 under the angle α in full lines wherein the deflectors16 and 17 are energized according to a first pattern, and FIG. 1 showsthe beam 13 in dotted lines to be incident under an opposite angle −αwhen the deflector 16 and 17 are energized by the controller 13according to a second pattern.

The electron beam column 1 also include a deflection system to scan thelocation 23 at which the beam 13 is incident on the surface 27 of thespecimen in directions transverse to the axis of symmetry 33. Thisdeflection system includes a deflector 35 which can be mounted withinthe objective lens 21 or at any other suitable position along the beampath.

The charged particle beam column 1 further includes a secondary particledetector 37 which is configured to detect secondary particles emergingfrom the specimen 29 and which are released therefrom by the incidentcharged particles of the beam 13. These secondary particles can be, forexample, secondary electrons. Detection signals generated by thedetector 37 are received by the controller 31.

The charged particle beam column 1 can be operated as a scanningmicroscope to record an image of the specimen as follows: the controller31 drives the deflector 35 such that the location 23 of incidence of abeam 13 on the specimen 29 is scanned across the surface 27, anddetection signals generated by detector 37 are recorded for each scanposition of location 23.

Further, multiple such images can be recorded for different angles α ofincidence of the beam 13 on the specimen 29 by changing the energizingpattern of the deflection system 15. A three-dimensional structure ofthe specimen 29 can be obtained from an analysis of two or more imagesobtained at different angles α of incidence.

At higher angles α of incidence, the beam 13 traverses the condenserlens 19 and the objective lens at a distance from the axis 33 ofsymmetry, and the beam 13 does also traverse portions of the condenserlens 19 and objective lens 21 at beam directions which are tiltedrelative to the axis 33 of symmetry. This has a consequence that thecondenser lens 19 and the objective lens 21 cause aberrations, such aschromatic aberrations and spherical aberrations, which distort the beamand can prevent a small focus diameter of the beam 13 at location 23. Tocompensate for such aberrations, the charged particle beam column 1includes an aberration corrector 41 controlled by the controller 31. Theaberration corrector 41 is schematically shown as a rectangle in FIG. 1.Such a corrector can include plural multipole lens elements, such asdisclosed, for example, in U.S. Pat. No. 7,223,983 B2. Exemplarysuitable correctors having plural multiple lens elements are disclosedin EP 0 451 370 A1, which is incorporated herein by reference in itsentirety. Suitable aberration correctors may include a mirror configuredto reflect the charged particle beam 13, such as disclosed, for example,in U.S. Pat. No. 5,319,207 A and U.S. Pat. No. 6,855,939 B2, each ofwhich is incorporated herein by reference in its entirety.

The aberration corrector 41 is energized by the controller 31 such thataberrations introduced by the condenser lens 19 and the objective lens21 are compensated for. To achieve the desired compensation, both thedeflection system 15 and the aberration corrector 41 are properlyadjusted. In some embodiments, this involves the following method: aspecimen having a flat structured surface is mounted relative to thecharged particle beam column 1 such that the surface of the specimencoincides with the object plane 25. The deflection system 15 isenergized such that the charged particle beam is subsequently incidenton the surface at multiple different tilt angles, and subsequently animage of the surface of the specimen is recorded as illustrated abovefor each setting of the tilt angle. Thereafter, an amount ofdisplacement of the structures of the sample shown in the image relativeto the structures in an image obtained at a tilt angle of α=0 isdetermined in dependence of the tilt angle α. If the deflection system15 and the aberration corrector 41 are not correctly adjusted, thedisplacements will increase with increasing tilt angle α. Herein, theincrease of displacement can be approximated by a sum of two components,where the first component increases linearly with the tilt angle and thesecond component increases with the third power of the tilt angle. Thedeflection system is adjusted by modifying the energization pattern forthe deflectors 16 and 17 such that the first component which increaseslinearly with the tilt angle vanishes. Thereafter, the energizationpattern applied to the aberration corrector 41 is varied such that thesecond component which increases with the third power of the tilt anglevanishes.

The aberration corrector 41 is energized such that aberrationsintroduced by components located downstream of the deflection system 15are compensated. In FIG. 1, the components downstream of the deflectionsystem 15 are the condenser lens 19 and the objective lens 21. Acomponent upstream of the deflection system 15 is the condenser lens 7.Also the condenser lens 7 introduces aberration on the charged particlebeam 13. However, these aberrations are not compensated by theaberration corrector. The fact that aberrations introduced by thecondenser lens 7 are not compensated by the aberration corrector 41adjusted as illustrated above can be shown as illustrated with referenceto FIG. 2 below.

FIG. 2 shows the charged particle beam column 1 of FIG. 1 wherein thedeflection system 15 is not energized such that the beam 13 is notdeflected by on the deflection system 15. A tilt angle β of the beam 13at the surface 27 of the specimen 29 is achieved by displacing theaperture plate 9 in a direction 45 such that the aperture 11 is locatedat a distance from the axis of symmetry 33. Due to the displacement ofthe aperture 11, the beam 13 traversing the aperture and shown in fulllines in FIG. 2 will be incident on the sample at a tilt angle β. Withthis configuration of the aperture plate 9, a first image is recorded asillustrated above. Thereafter, the aperture plate 9 is displaced suchthat the aperture 11 is located on the other side of the axis 33 ofsymmetry such that a beam 13′ shown in broken lines in FIG. 2 traversesthe aperture plate 9 and is incident on the surface of the specimenunder an angle −β which is opposite to the angle of incidence for thefirst image. With this configuration, a second image is recorded. If theaberration corrector is adjusted to compensate for aberrationsintroduced by the condenser lens 19 and the objective lens 21 while notcompensating for aberrations introduced by the condenser lens 7,structures of the sample will be visible at different displacedlocations in the two recorded images.

It is therefore possible to distinguish an aberration corrector adjustedas described herein from an aberration corrector adjusted such that itcompensates aberrations introduced by the objective lens 21 and bothcondenser lenses 7 and 19. If the two images illustrated with referenceto FIG. 2 were recorded with an aberration corrector that compensatesaberrations for objective lens 21 and both condenser lenses 7 19,structures of specimen would be visible in both images at samelocations.

While certain exemplary embodiments are disclosed herein, alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, the exemplary embodiments set forth herein areintended to be illustrative and not limiting in any way. Various changesmay be made without departing from the spirit and scope of the presentdisclosure.

What is claimed is:
 1. A system, comprising: an objective lensconfigured to focus a charged particle beam in an object plane; a firstcondenser lens disposed in a beam path of the charged particle beamupstream of the objective lens; a deflector disposed in the beam pathbetween the first condenser lens and the objective lens, the deflectorconfigured to change an angle of incidence of the charged particle beamin an object plane; a second condenser lens disposed in the beam pathbetween the deflector and the objective lens; and an aberrationcorrector disposed in the beam path between the deflector and theobjective lens, the aberration corrector configured to compensateaberrations introduced by the objective lens, wherein: the aberrationcorrector is configured to not compensate aberrations introduced by thefirst condenser lens; the aberration corrector is configured to correctaberrations introduced by the second condenser lens; and the system is acharged particle beam system.
 2. The system according to claim 1,further comprising a beam scanner disposed in the beam path between theaberration corrector and the object plane, wherein the beam scanner isconfigured to scan a location of incidence of the charged particle beamacross the object plane.
 3. The system according to claim 2, wherein theaberration corrector comprises a plurality of multipole lens elements.4. The system according to claim 2, wherein the aberration correctorcomprises a mirror configured to reflect the charged particle beam. 5.The system according to claim 2, further comprising a charged particlebeam source, wherein the first condenser lens is disposed in the beampath between the objective lens and the charged particle beam source. 6.The system according to claim 1, wherein the aberration correctorcomprises a plurality of multipole lens elements.
 7. The systemaccording to claim 1, wherein the aberration corrector comprises amirror configured to reflect the charged particle beam.
 8. The systemaccording to claim 1, further comprising a charged particle beam source,wherein the first condenser lens is disposed in the beam path betweenthe objective lens and the charged particle beam source.
 9. A method,comprising: condensing a charged particle beam while introducing firstaberrations into the charged particle beam to provide a first condensedcharged particle beam; deflecting the condensed charged particle beam toprovide a deflected charged particle beam; condensing the deflectedcharged particle beam while introducing second aberrations on the beam;focusing the deflected charged particle beam on a specimen whileintroducing third aberrations into the deflected charged particle beam;and compensating the second and third aberrations while leaving thefirst aberrations uncompensated to provide a compensated chargedparticle beam.
 10. The method according to claim 9, further comprisingscanning a location of incidence of the compensated charged particlebeam across the specimen.
 11. The method according to claim 9, furthercomprising using a charged particle source to provide the chargedparticle beam.
 12. The method according to claim 9, comprising using anaberration corrector to compensate the second and third aberrations,wherein the aberration corrector comprises a plurality of multipole lenselements.
 13. The method according to claim 9, comprising using anaberration corrector to compensate the second and third aberrations,wherein the aberration corrector comprises a mirror configured toreflect the charged particle beam.
 14. A system, comprising: anobjective lens configured to focus a charged particle beam in an objectplane; a deflector disposed in a beam path of the charged particle beamupstream of the objective lens; a first condenser lens disposed in abeam path of the charged particle beam system upstream of the deflector;a second condenser lens disposed in the beam path of the chargedparticle beam downstream of the deflector; and an aberration correctordisposed in the beam path between the deflector and the objective lens,wherein the aberration corrector is configured to compensate aberrationsintroduced by components located in the beam path downstream of thedeflector without compensating aberrations introduced by componentslocated in the beam path upstream of the deflector, and the system is acharged particle beam system.
 15. The system according to claim 14,further comprising a charged particle beam source, wherein the deflectoris disposed in the beam path between the objective lens and the chargedparticle beam source.
 16. The system according to claim 14, wherein theaberration corrector comprises a plurality of multipole lens elements.17. The system according to claim 14, wherein the aberration correctorcomprises a mirror configured to reflect the charged particle beam. 18.The system according to claim 14, further comprising a charged particlebeam source upstream, wherein the first condenser lens disposed in thebeam path between the objective lens and the charged particle beamsource.